1. Field of the Invention
The present invention relates to an ignition apparatus for an internal combustion engine having a power switch for intermittently feeding a primary current to an ignition coil, the power switch being contained in an insulating case and fixed therein by an insulating resin material poured into the insulating case.
2. Description of the Related Art
FIG. 6 is a partial cross sectional view of a conventional ignition apparatus for an internal combustion engine, FIG. 7 is an overall perspective view of an insulating case and FIG. 8 is an electric circuit diagram of the ignition apparatus for the internal combustion engine. In the drawings, a hole (not shown) is defined at the center of bottom of the accommodating portion 1a of a synthetic resin insulating case 1. A first E-shaped iron core 2 of an ignition coil passes through the hole at the central portion thereof. A second E-shaped iron cone 3 of the ignition coil is spaced apart from the first E-shaped iron core 2. A primary coil 4 is wound around the central portion of the first E-shaped iron core 2 and the central portion of the second E-shaped iron core 3 spaced apart from the first E-shaped iron core in confrontation therewith. A secondary coil 5 is wound around the outer periphery of the primary coil 4.
A power switch 6 is accommodated in an auxiliary accommodating portion 1c projecting from the accommodating portion 1a. The power switch 6 includes a tray shaped copper heat sink 7, a switching device 8 which is a power transistor accommodated in the heat sink 7, a hybrid integrated circuit (hybrid IC) 9 for driving and controlling the switching device 8, a electrical wire conductor 10 for connecting the switching device 8 to the hybrid integrated circuit 9, a wire conductor 11 having an end connected to the hybrid integrated circuit 9 and a silicone gel 12 filled into the heat sink 7 for protecting a switching unit composed of the switching device 8 and the hybrid integrated circuit 9.
The insulating case 1 includes a holding portion 1d for a high-tension terminal as the high-tension unit of an ignition coil (not shown) and a holding portion 1e for a low-tension terminal unit. The low-tension terminal unit includes a VB terminal 13a for connecting the primary coil to the battery of an automobile, an ignition signal input terminal 13b for imposing an ignition signal from a control unit (not shown) to the power switch 6 and a ground terminal 13c.
In the ignition apparatus for the internal combustion engine arranged as described above, the power switch 6 having the heat sink 7 into which the silicone gel 12 is filled is accommodated in the auxiliary accommodating portion 1c and then the extreme end of the wire conductor 11 is connected to the terminals 13b, 13c as well as the power switch 6 is connected to the primary coil 4 through the wire conductor 15. Thereafter, the accommodating portion 1a and auxiliary accommodating portion 1c of the insulating case 1 is filled with an electrically insulating resin 14 and the insulating resin 14 is cured so as to fix the power switch 6 in the insulating case 1.
With this arrangement, a primary current flowing to the primary coil 4 of the ignition coil is controlled through the power switch 6 in response to an ignition signal input from an ignition signal input terminal 13b. A high-tension voltage is produced to the secondary coil 5 of the ignition coil in response to the primary current flowing to the primary coil 4 and fed to a distributor (not shown) through the high-tension terminal.
In the conventional ignition apparatus for the internal combustion engine, the insulating resin 14 is repeatedly expanded and contracted by the effect of the heat produced in the secondary coil 5 and the switching device 8 by the intermittent operation of the power switch 6, by which tension is applied to the wire conductors 11 and 15. As a result, the bonded portion 11a of the wire conductor 11 is exfoliated from the hybrid integrated circuit 9, for example, whereby a problem arises in a heat shock resistant performance.
Likewise, there is also a problem that when a job for assembling the power switch 6 into the insulating case 1 or connecting the wire conductor 11 is carried out, stress such as tension or the like is applied to the wire conductor 11, so that the bonded portion 11a of the wire conductor 11 is exfoliated from the hybrid integrated circuit 9, and working reliability is lost.
Further, there is a problem that when the insulating resin 14 is poured into the insulating case 1 in vacuum, air contained in the silicone gel 12 moves into the insulating resin 14 to form voids in the insulating resin 14 so that the insulating performance of the insulating resin 14 is deteriorated.